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On 11 January 1922 , a fourteen - year - old boy called Leonard Thompson was lying in Toronto General Hospital . He had had diabetes for about three years , and he weighed only 65 pounds , about 30 kilograms . In diabetes , the level of sugar in the blood becomes dangerously high . The cause is a problem with insulin , a hormone that is made by the pancreas . Insulin tells the body to store sugar in the muscles , the liver and fat . Before insulin , the kind of diabetes Leonard had was almost always fatal , and doctors could offer little more than a strict diet . The answer came from a laboratory at the University of Toronto . In 1921 a doctor , Frederick Banting , and a student , Charles Best , worked there under the professor John Macleod . They took an extract from the pancreas of dogs and used it to treat a dog with diabetes . Leonard 's father agreed to try their extract . The first injection , on 11 January , was a disappointment . The extract was impure , and the dose was too small . His blood sugar fell by about a quarter , but he was still seriously ill , and an abscess grew where the needle went in . Macleod had asked a chemist , James Collip , to make the extract purer . Within weeks he succeeded . On 23 January , Leonard received Collip 's purer extract , and his blood sugar soon fell to a normal level . His condition improved quickly . After the success of Leonard and other early patients , many people with diabetes wrote to Toronto asking for insulin . In 1923 Banting and Macleod received the Nobel Prize in Medicine . Leonard lived for thirteen more years with insulin and died in 1935 , at the age of 27 . Leonard 's kind of diabetes became an illness that people could live with . Today millions of people still rely on insulin , and the first of them was one boy in a Toronto hospital bed . 
